1. Field of the Invention
The present invention relates to a wireless IC device and, more particularly, to a wireless IC device that has a wireless IC used in an RFID (Radio Frequency Identification) system, and an electronic apparatus.
2. Description of the Related Art
In recent years, an RFID system has been developed as an article management system, which includes a reader/writer that generates an induction field and an IC chip (also referred to as IC tag or wireless IC chip) that stores predetermined information allocated to an article or a casing, and non-contact communication is established between the reader/writer and the IC chip to transmit the information therebetween.
A known existing wireless IC device equipped with an IC chip includes a wireless IC tag as described in Japanese Unexamined Patent Application Publication No. 2005-244778. In the wireless IC tag, a dipole antenna (formed of a pair of main antenna elements and matching sections) is provided on a dielectric substrate, and a tag IC is electrically connected to an end portion of the dipole antenna. The matching section is arranged between the tag IC and each main antenna element and has the function of matching impedance therebetween.
However, the above wireless IC tag has the following problems. First, because each matching section and the corresponding main antenna element are formed adjacent to each other on a single substrate, the size of the wireless IC tag increases. Second, it is necessary to mount a small wireless IC chip on an electrode formed on a large substrate on which the main antenna elements and the matching sections are arranged, so a highly accurate mounter is required. In addition, it requires time for positioning at the time of mounting, so manufacturing time is increased, and cost for the wireless IC tag increases. Third, because the main antenna elements and the wireless IC chip are connected in an electrically conductive state, so there is a possibility that the wireless IC chip may be damaged when static electricity enters from the main antenna elements.
In addition, Japanese Unexamined Patent Application Publication No. 2000-311226 describes a wireless IC card. The wireless IC card uses an IC chip in which an antenna coil is formed on the surface of the IC chip. In the above wireless IC card, a first antenna coil formed on the IC chip is coupled to a second antenna coil formed on a module substrate through a magnetic field.
However, in the wireless IC card described in Japanese Unexamined Patent Application Publication No. 2000-311226, it is necessary to accurately control the interval between the first and second antenna coils to a size at which a desired coupling is achieved. Specifically, as described in the paragraph [0107] of Japanese Unexamined Patent Application Publication No. 2000-311226, it is necessary to set the interval to a smaller interval that is smaller than or equal to 20 μm. When the two antenna coils are coupled with the above small interval, there is a problem that slight variations in the amount or dielectric constant of insulating adhesive arranged between the two antenna coils and in between each antenna coil vary a coupled state and, therefore, the radiation characteristic of the wireless IC card decreases. In addition, in order to mount the IC chip on the module substrate at a small interval with high accuracy, it requires an expensive mounter, and, as a result, cost for the wireless IC card increases.